feat(database): inline embed + Open button + side peek + title placeholder

- Page title placeholder: new pages created with empty title, CSS :empty::before shows 'New page' in gray
- Database is now inline embed within page (not full-page replacement)
- Embed block 'collection' renders database table via FlowDeckDB.renderInto()
- Open button in column 1 of each row opens page in side peek panel
- Side peek: iframe loading /pages/{id}?embed=1, close/fullscreen/resize
- DB scripts refactored as reusable DBInstance + global FlowDeckDB API

app/routers/board.py

@@ -814,7 +814,7 @@ async def create_page(request: Request, title: str = Query(default=""),
     """Create a new Markdown page, optionally as a sub-page."""
     user = SessionManager.decode_session(request.cookies.get("flowdeck_session", ""))
     ws_key = project if project else (user.get("login", "Bruno") if user else "Bruno")
-    page_title = title.strip() if title else "Untitled"
+    page_title = title.strip() if title else ""
     try:
         with get_conn() as conn:
             # Compute next sort_order for this parent